1. Field of the Invention
The present invention relates to composite modules provided with a wiring substrate including wiring electrodes provided inside and on a main surface thereof.
2. Description of the Related Art
With cellular phones becoming smaller in size and thickness, composite modules mounted therein are being required to be reduced in size and lowered in profile these days. As such, wiring substrates included in composite modules are made smaller in size and thickness, and various types of circuits are configured such that wiring electrodes, ground electrodes, and so on that constitute inductors, capacitors, and the like are so disposed as to be close to one another on each wiring substrate, whereby reduction in size and lowering in profile of the composite modules are realized. However, when the electrodes are disposed close to one another as described above, undesired stray capacitance and the like are produced between the wiring electrodes and the ground electrodes constituting inductor elements, for example. This causes a problem that frequency characteristics of the inductor elements are deteriorated and characteristic impedance of the wiring electrodes defined between the wiring electrodes and the ground electrodes cannot have a predetermined value.
As a known technique, as shown in FIG. 5, a high frequency module 200 is proposed in which a cutout 204 is provided in a ground electrode 202, which is formed inside a wiring substrate 201, at a portion thereof overlapping with an inductor element 203 when viewed from above (see, for example, paragraphs [0059] to [0063] and FIG. 7 of Japanese Unexamined Patent Application Publication No. 2006-33211). This technique makes it possible to reduce stray capacitance produced between the ground electrode 202 and the inductor element 203 so that the frequency characteristics of the inductor element 203 can be prevented from being deteriorated.
Note that, however, in the case where the cutout 204 is provided in the ground electrode 202 in the manner as seen in the known technique, a portion of the ground electrode 202 to shield the inductor element 203 is not present. This causes a risk that when the high frequency module 200 is mounted on a mother board, for example, signals leaked from other elements, modules, and so on formed on the mother board interfere with the inductor element 203 so that the frequency characteristics and the like of the high frequency module 200 are deteriorated.
Further, in order to provide the cutout 204 in the ground electrode 202 at a portion thereof corresponding to the inductor element 203, the ground electrode 202 is removed considerably, causing the area of the ground electrode 202 to be smaller. As a result, inductance that is parasitically present on wiring for connecting electronic components mounted on the wiring substrate 201 with the ground electrode 202 increases.